This proposal outlines a basic research plan for studying the mechanism of regulation of muscle contraction as mediated by calcium- binding proteins. In particular, the structural and functional rela- tionship between mammalian troponin A and the muscle calcium-binding proteins (MCBP) from the lower vertebrates will be investigated with the idea of using MCBP as a model system for clarifying the nature of the regulatory processes of muscle contraction. The unique similarities between troponin A and MCBP, although not definitive, are highly suggestive that these proteins are both structurally and functionally homologous. The detailed structure of MCBP which is currently available (complete amino acid sequence and three-dimensional structure of 2A resolution) provides an excellent basis for defining functional and regulatory properties in terms of detailed structural features.